1. Field of the Invention
This invention is in the field of articles which retain liquids therein and more particularly relates to porous shaped bodies capable of retaining liquids in a manner which allows the liquids to be controllably dispensed upon the application of pressure to the shaped body.
2. Description of the Prior Art
The desirability of providing porous bodies capable of imbibing, retaining, and subsequently controllably dispensing liquids has been recognized for many years. Such bodies are useful wherever a liquid is to be applied to a receptor surface in limited amounts. Thus, these bodies would be useful, for example, in the application of water to a remoistenable adhesive layer on labels, stamps, envelope flaps, and the like; the application of medicaments or lotions to the body; the application of ink to printing devices; and the application of ink directly to an article or sheet to be marked as with an inked stamp.
There has been a particularly high level of interest in producing such porous bodies which would serve as printing stamps or stamp pads. Bodies suitable for such applications generally consist of a resilient microporous material having a surface corresponding to the character to be printed; they contain a reservoir of ink which is conducted to their surface through the porous structure. Two relatively recent attempts to produce porous applicator structures useful for printing stamps are described in U.S. Pat. Nos. 3,019,201 and 3,755,517, both issued to Clancy et al.
In U.S. Pat. No. 3,019,201, a novel type of applicator structure is described which is capable of retaining a relatively large quantity of liquid which can be delivered from the surface in controlled amounts and in which the supply of liquid can be replenished. Briefly, the method described in this patent comprises binding together loosely packed, generally spherical particles of a resilient material, preferably an elastomer, to produce a porous structure having a continuous interstitial phase, consisting predominantly of the voids that would naturally occur between the packed particles making up the structure. In use, the interstitial regions of the applicator structure contain a supply of the liquid to be fed through the applicator to its applying surface, whether or not the surface is molded to a desired configuration. These interstitial regions are accordingly of capillary dimensions, which render them capable of retaining the liquid. The particles making up the porous structure must be of a material which will be wetted by the liquid to be retained and subsequently delivered at a controlled rate when the porous structure is brought into pressure contact with a receptor surface.
The steps employed to effect the necessary bonding of particles in the process of U.S. Pat. No. 3,019,201 consist of washing or air-cleaning the elastomeric particles to remove any films or particulate material, adding the cleaned rubber-like particles to an alcohol solution of resin binder (which may also contain a semi-solvent or a softening agent for the rubber-like particles), pouring the resultant slurry or paste into a mold, expressing excess liquid from the slurry in the mold, driving off any residual liquid with heat, and curing the structure either within or outside the mold.
The process of U.S. Pat. No. 3,755,517 is similar but provides improved porosity by adding the additional step of incorporating water into the slurry of rubber-like particles to produce a dispersion. This dispersion can then be cast to form a wet structure which is subsequently dried with or without curing. The cast structure can be stored for relatively long periods and subsequently molded just prior to use to produce a final product having a surface with a predetermined configuration. This product is particularly suited as a self-inking printing stamp.
Although the latter process resulted in some improvement, it should be noted that it is primarily directed to producing an intermediate product which can be stored for reasonably long periods of time and subsequently molded with pressure and/or heat into a final configuration. In many applications, however, it is desirable to have a process capable of producing a finished, more intricately shaped product without the necessity of a final molding step. This process should be continuous and efficient, and should produce a final shaped body, as opposed to an intermediate article, which has an excellent balance of porosity and strength. Such a process would lend itself to the efficient, economical production of final, porous, shaped bodies which consistently have the properties desired to retain and subsequently controllably dispense a wide variety of liquids.